In a current wireless network system, to reduce interference between different wireless technologies, national and governmental agencies allocate some spectrums to specified agencies to provide services. Specified and allocated spectrums are referred to as licensed spectrums, and unspecified and unallocated spectrums are referred to as unlicensed spectrums. With development of communications technologies, to better meet requirements for mobile broadband services, unlicensed spectrum resources start to be used to perform data transmission.
There is a time limit on data transmission performed in an unlicensed spectrum, and after a time during which a device occupies a channel in the unlicensed spectrum reaches a maximum limit, the occupied unlicensed spectrum needs to be released for a period of time. Before the device occupies the channel in the unlicensed spectrum next time, the device needs to listen on the channel to determine whether the channel is idle.
In an HARQ (Hybrid Automatic Repeat Request) technology, by means of flexible mapping between carriers, cross-carrier retransmission of data is implemented, which can resolve a problem caused when a device does not complete data transmission in an unlicensed spectrum within a regulated occupation time. For example, data transmitted on a carrier A is not completed in the unlicensed spectrum within the regulated time, the data transmitted on the carrier A is retransmitted on a carrier B. However, in the prior art, a dedicated field is added to downlink data scheduling signaling to instruct to retransmit data, which increases overheads of downlink scheduling signaling.